Resin dispersion for cationic electrodeposition and cationic electrodeposition coating composition including the same

ABSTRACT

Disclosed are a resin dispersion and a cationic electrodeposition coating composition including the same, in which the dried coating film of the electrodeposition paint is lead-free and has an epoxy-acrylic double-layered structure for displaying excellent properties, and in which an organic solvent content can be minimized. A resin dispersion of a cationic electrodeposition includes an aqueous dispersion prepared by the following processes. The resin dispersion includes a cationic electrodeposition resin, deionized water, an acid for neutralization, a reaction product of manganese phosphate and an acid diluted in an deionized water to 10%, and a cationic surfactant. The cationic electrodeposition resin can be prepared in the presence of an organic solvent from (a) a cationic electrodeposition synthetic resin produced by an epoxy-amino addition reaction (b) an acrylic cationic electrodeposition resin having an amino group (c) a fatty acid ester resin synthesized by an esterfication reaction of styrene-allylalcohol copolymer and fatty acid and (d) blocked polyisocyanatecuring agent. The cured film has an epoxy-acrylic double-layered structure to give a high functionality, for improving properties such as weather-resistance, yellowing resistance, etc.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a resin dispersion for cationicelectrodeposition and a cationic electrodeposition coating compositionincluding the same, and more particularly to a lead-free cationicelectrodeposition coating composition in which the electrodepositedcoating film thereof has an epoxy-acrylic double-layered structure togive a high functionality, and in which an organic solvent content isminimized.

2. Description of the Related Arts

Since electrodeposition coating has a good efficiency in application anda high corrosion-resistance and can minimize an environmentalcontamination because of employing water as a solvent, it is widely usedfor primer coating of cars, household electric appliances, andindustrial machines when comparing with a brush coating or a spraycoating. Recently and widely used epoxy-based cationic electrodepositioncoating composition includes cationic epoxy resin onto which amine isadded and blocked polyisocyanate. Researches at home and abroad oncationic electrodeposition paint are concentrated on paints related toenergy conservation, safety, and environmental considerations. Also,researches on electrodeposition coating composition are concentrated ondeveloping highly functional and highly efficient electrodepositionpaint having various purposes and characteristics.

Generally, a catonic electrodeposition coating composition includes atin compound such as dibutyl tin oxide in order to improve across-inking reaction between a compound containing hydroxyl functionalgroup with a compound containing isocyanate functional group, along witha lead compound as an anticorrosive pigment in order to improve acorrosion-resistance. However, the lead compound becomes a target ofrestriction on usage in all over the world as a material inducing anenvironmental contamination. In July 1996, in Japan, an automobileindustrial institute established an independent restriction law named asSHREDDER DUST and suggested each automobile manufacturing company tolessen the utilizing amount of lead in the automobiles. In Europe (EU),a law to restrict on crushing, reclamation, incineration of anautomobile containing harmful materials such as lead, cadmium, mercury,etc. after completing the operation of the automobile, will bepositively established since 2003. Therefore, with the movements onrestricting the environmental pollutants, researches on reducing orremoving the harmful materials such as lead from a coated and dried filmof the electrodeposition coating composition are actively progressed.

U.S. Pat. No. 5,908,912 (issued to Kollah et al.) discloses a formationof a lead-free dried film by applying a salt of bismuth compound and acarboxylic acid including amine into a pigment paste as a reactioncatalyst for preparing a cationic electrodeposition coating composition.In addition, disclosed are the problems of coagulation of the bismuthsalt during storage and a lowering of the pH of the electrodepostioncoating composition because of the addition of a large amount of an acidin order to applying the bismuth compound into the cabonicelectrodeposition coating composition.

Among the researches, studies on reducing an organic solvent emissionduring coating operations are being developed. The motive for thesestudies is the regulation of emission of organic solvents for theprotection of the environment. As examples of the regulations related tothe regulation of emission of organic solvents, the regulation forvolatile organic compounds (VOC) of the Environment Office in U.S. andthe atmospheric purification law (TA-Luft) in Germany can be noted. Theformer establishes a guideline for the emission amount of the organicsolvents from a coating composition, while the latter restricts thetotal amount of the organic solvents discharged from the paint consumedfor coating one car. Since about 20% of the total amount of carbondioxide discharged Into the world is due to the coating industry (forexample, organic solvent and combustion by means of a drying oven), thecoating industry is a major cause of the environmental pollution. Hence,the coating industry has become the subject of supervision.

Presently, as an electrodeposition coating composition of primercoating, an epoxy cationic electrodeposition paint is mainly used.However, the epoxy cationic electrodeposition paint is rich in organicsolvents and these solvents are evaporated from the electrodepositiontank, thereby emitting an offensive odor from a work-piece. Also, thesesolvents are emitted during curing and drying, so environmentalpollution problems occur. In U.S. Pat. No. 6,147,144, (issued to thepresent inventors), a cationic electrodeposition coating composition Inwhich the amount of the organic solvent is minimized, is disclosed.

Further, even though the conventional epoxy cationic electrodepositionpaint has a good corrosion-resistance and a good adherence, this islacking in properties such as a weather-resistance, a yellowingresistance, etc.

SUMMARY OF THE INVENTION

It is an object in the present invention considering the conventionalproblems, to provide a resin dispersion of a cationic electrodeposition,of which dried film is free from lead, and which includes a minimizedamount of organic solvents and has an epoxy-acrylic double-layeredstructure to improve a weather-resistance and a yellowing resistance,and a method of preparing thereof.

Another object of the present invention is providing a pigment pastecomposition which can produce a lead-free cationic electrodepositioncoating composition appropriate for implementing an electrodeposition.

Further another object of the present invention is providing a cationicelectrodeposition coating composition including the above-describedresin dispersion of the cationic electrodeposition and pigment pastecomposition, and a method of preparing thereof.

To accomplish the object, there is provided in the present invention aresin dispersion of a cationic electrodeposition including an aqueousdispersion. The aqueous dispersion is prepared by mixing about 35-45parts by weight of a cationic electrodeposition resin, about 55-65 partsby weight of deionized water, about 0.3-1.5 parts by weight of an acidfor neutralization, about 1-5 parts by weight of a reaction product ofmanganese phosphate and an acid diluted in an deionized water to 10% andabout 0.5-1 parts by weight of a cationic surfactant.

The cationic electrodeposition resin is prepared in the presence of anorganic solvent from (a) about 40-60% by weight of a cationicelectrodeposition synthetic resin produced by an epoxy-amino additionreaction (b) about 5-10% by weight of an acrylic cationicelectrodeposition resin having an amino group (c) about 1-3% by weightof a fatty acid ester resin synthesized by an esterification reaction ofstyrene-allylalcohol copolymer and fatty acid and (d) about 30-50% byweight of blocked polyisocyanate curing agent.

The resin dispersion of the cationic electrodeposition is prepared bythe following method including the steps of preparing a cationicelectrodeposition resin, preparing an aqueous dispersion, removingorganic solvents having a low boiling point from the aqueous dispersionby extracting and then filtering.

The cationic electrodeposition resin is prepared in the presence of anorganic solvent from (a) about 40-60% by weight of a cabonicelectrodepositon synthetic resin produced by an epoxy-amino additionreaction (b) about 5-10% by weight of an acrylic cationicelectrodeposition resin having an amino group (c) about 1-3% by weightof a fatty acid ester resin synthesized by an esterification reaction ofstyrene-altylalcohol copolymer and fatty acid and (d) about 30-50% byweight of blocked polyisocyanate curing agent. The aqueous dispersion isprepared by mixing about 35-45 parts by weight of the cationicelectrodeposition resin, about 55-65 parts by weight of deionized water,about 0.3-1.5 parts by weight of an acid for neutralization, about 1-5parts by weight of a reaction product of manganese phosphate and an aciddiluted in an deionized water to 10% and about 0.5-1 parts by weight ofa cationic surfactant.

Preferably, a solid content in the resin dispersion of the cationicelectrodeposition is about 30-40% by weight and a mean size of particlescontained in this dispersion is about 60 nm or less. A preferred amountof organic solvents in this dispersion is about 0.5% by weight or less.

The other object of the present invention is accomplished by a pigmentpaste composition including (a) about 15-30% by weight of pigmentgrinding vehicle (b) about 2-6% by weight of an anticorrosive pigmentand (c) about 0.7-2.3% by weight of dibutyl tin oxide. The ratio ofsolid content of the pigment/pigment grinding vehicle is in a range ofabout 1/0.2-1/0.45.

Particularly, the pigment grinding vehicle is obtainable from about25-35% by weight of polyglycidyl ether of bisphenol A, about 5-12% byweight of propyleneglycol monomethyl ether acetate, about 8-15% byweight of partially blocked isocyanate cross-linking agent, about 25-40%by weight of ethylene glycol monobutyl ether, about 10-20% by weight oforganic tertiary amino acid salt and about 0-5% by weight of deionizedwater. Further, the epoxy equivalent weight of the polyglycidyl ether ofbisphenol A is in a range of about 900-1200.

In addition, the preferred anticorrosive pigment is at least oneselected from the group consisting of bismuth hydroxide, bismuthtrioxide, bismuth oxide, aluminum tri-polyphosphate hydrate andmagnesium aluminum hydroxide carbonate hydrate.

Further another object of the present invention is accomplished by acationic electrodeposition coating composition comprising an aqueousdispersion and a pigment paste composition. The aqueous dispersion isprepared by mixing about 35-45 parts by weight of a cabonicelectrodeposition resin, about 55-65 parts by weight of deionized water,about 0.3-1.5 parts by weight of an acid for neutralization, about 1-5parts by weight of a reaction product of manganese phosphate and an aciddiluted in an deionized water to 10% and about 0.5-1 parts by weight ofa cationic surfactant.

The cationic electrodeposition resin is prepared in the presence of anorganic solvent from (a) about 40-60% by weight of a cationicelectrodeposition synthetic resin produced by an epoxy-amino additionreaction (b) about 5-10% by weight of an acrylic cationicelectrodeposition resin having an amino group (c) about 1-3% by weightof a fatty acid ester resin synthesized by an esterification reaction ofstyrene-allylalcohol copolymer and fatty acid and (d) about 30-50% byweight of blocked polyisocyanate curing agent.

A method of preparing the cationic electrodeposition coating compositionalso is provided in the present invention. The cationicelectrodeposition coating composition is prepared by preparing acationic electrodeposition resin, preparing an aqueous dispersion,preparing a resin dispersion of a cationic electrodeposition by removingorganic solvents having a low boiling point from the aqueous dispersionby extracting and then filtering, and then mixing thus obtained cationicelectrodeposition resin dispersion with a pigment paste composition.

The cationic electrodeposition resin is prepared in the presence of anorganic solvent from (a) about 40-60% by weight of a cationicelectrodeposition synthetic resin produced by an epoxy-amino additionreaction (b) about 5-10% by weight of an acrylic cationicelectrodeposition resin having an amino group (c) about 1-3% by weightof a fatty acid ester resin synthesized by an esterification reaction ofstyrene-allylalcohol copolymer and fatty acid and (d) about 30-50% byweight of blocked polyisocyanate curing agent.

The aqueous dispersion is prepared by mixing about 35-45 parts by weightof the cationic electrodeposition resin, about 55-65 parts by weight ofdeionized water, about 0.3-1.5 parts by weight of an acid forneutralization, about 1-5 parts by weight of a reaction product ofmanganese phosphate and an acid diluted in an deionized water to 10%,and about 0.5-1 parts by weight of a cationic surfactant.

Further another object of the present invention also can be accomplishedby a cationic electrodeposition coating composition including a pigmentpaste composition comprising (a) about 15-30% by weight of pigmentgrinding vehicle (b) about 2-6% by weight of an anticorrosive pigmentand (c) about 0.7-2.3% by weight of dibutyl tin oxide. The ratio ofsolid content of the pigment/pigment grinding vehicle is in a range of1/0.2-1/0.45.

DETAILED DESCRIPTION OF THE INVENTION

The cationic electrodeposition resin applicable in the present inventionis a major component for forming a film in the electrodeposition coatingcomposition. Some of these known cationic electrodeposition resin areillustrated in U.S. Pat. Nos. 3,663,839; 3,984,299; 3,947,338;3,947,339; and 6,130,274. These film forming resins represent a resinhaving an amino group formed by an addition reaction of polyepoxide witha primary, secondary, or tertiary amine. In the present invention, asfor the cationic electrodeposition synthetic resin formed by an additionreaction of polyepoxide and amine a resin having the followingstructural formula can be illustrated:

In the above-illustrated structure, R₁, R₂ and B are as follows and n isan integer of 3 or 4.

R₁ R₂ B N-methyl ethanol amine —CH₃ —(CH₂)₂OH

diketimine

R₂═R₁

If the amount of the cationic electrodeposition synthetic resin havingan amino group used is less than 40% by weight, mechanical properties ofthe dried coating layer are weak, and if the amount of the cationicelectrodeposition synthetic resin used exceeds 60% by weight, themanufacture of an aqueous dispersion is difficult. Therefore, the amountof the cationic electrodeposition resin having an amino group used ispreferably in the range of about 40-60% by weight, and more preferablyabout 45-55% by weight.

In addition, as another cationic electrodeposition resin, an acryliccationic electrodeposition resin having an amino group which iscopolymerized with butyl acrylate, methyl acrylate, hydroxy ethylacrylate, styrene, methyl methacrylate, (N,N-dimethyl)aminoethylmetacrylate, etc., can be illustrated.

If the amount of the acrylic cationic electrodeposition resin used isless than 5% by weight, a dried coating film having an epoxy-acrylicdouble layered structure cannot be obtained, and if the amount of theacrylic cationic electrodeposition resin used exceeds 10% by weight, theepoxy resin and acrylic resin are not compatible, thereby affecting thesurface appearance and gloss. Therefore, the amount of the acryliccationic electrodeposition resin used is preferably in the range ofabout 5-10% by weight, and more preferably about 7-9% by weight.

Usually these resins having an amino group are used together with ablocked polyisocyanate curing agent. Isocyanate is so completely blockedthat it can be mixed with the resin having an amino group. Otherwise,isocyanate is partially blocked in such a manner that it can react withthe backbone of a resin. As for the blocked polyisocyanate curing agent,the compounds having the following structural formulae can beillustrated:

If the amount of the blocked polyisocyanate curing agent used is lessthan 30% by weight, properties such as pencil hardness,corrosion-resistance, etc., are diminished. If the amount of the blockedpolyisocyanate curing agent used exceeds 50% by weight, the preparationof an aqueous dispersion is difficult and properties such asimpact-resistance, flexible-resistance, etc., are diminished. Therefore,the amount of the blocked polyisocyanate curing agent used is preferablyin the range of about 30-50% by weight, and more preferably 35-45% byweight.

Particularly, the composition of the present invention comprises a fattyacid ester synthetic resin synthesized by an ester reaction ofstyrene-allylalcohol and fatty acid, in order to improve a smoothness ofthe electrodeposited coating film and to inhibit a pinhole and crateringcharacteristic. As for the fatty acid ester synthetic resin, a resinhaving the following structural formula can be illustrated:

The molecular weight (weight-average molecular weight) of these fattyacid ester resins is preferably in the range between about 2000-40,000,and more preferably is between about 3000-30,000. If the amount of thesefatty acid ester resins used is less than 1% by weight, an improvementof the smoothness of the electrodeposited coating film and the restraintof the pinhole and cratering characteristic cannot be achieved. However,if the amount of these fatty acid ester resins used exceeds 3% byweight, mechanical properties of the dried coating film such as pencilhardness is deteriorated. Therefore, the amount of the fatty acid esterresin used is preferably in the range of about 1-3% by weight, and morepreferably about 1.5-2.5% by weight.

The method of preparing the cationic electrodeposition coatingcomposition according to the present invention will be described indetail below.

First, a cationic electrodeposition resin is prepared in the presence ofan organic solvent having a low boiling point of about 140° C. or lessfrom (a) about 40-60% by weight of a cationic electrodepositionsynthetic resin produced by an epoxy-amino addition reaction (b) about5-10% by weight of an acrylic cationic electrodeposition resin having anamino group (c) about 1-3% by weight of a fatty acid ester resinsynthesized by an esterification reaction of styrene-allylalcoholcopolymer and fatty acid and (d) about 30-50% by weight of blockedpolyisocyanate curing agent. As the organic solvents having the lowboiling point, methyl isobutyl ketone, xylene, toluene, methyl ethylketone, etc. can be illustrated.

The cationic electrodeposition synthetic resin obtained by anepoxy-amino addition reaction may be manufactured by using an epoxyresin, polycaprolactonediol, bisphenol A, and benzyl dimethyl amine.

Thereafter, about 35-45% by weight of thus prepared cationicelectrodeposition resin, about 55-65 parts by weight of deionized water,about 0.3-1.5 parts by weight of an acid for neutralization, about 1-5parts by weight of a reaction product of manganese phosphate and an aciddiluted in an deionized water to 10% , and about 0.5-1 parts by weightof a cationic surfactant, are mixed to prepare an aqueous dispersion.The aqueous dispersion is extracted under reduced pressure to remove theorganic solvents having the low boiling point. In the following, theaqueous dispersion is filtered to prepare the cationic electrodepositioncoating composition.

During the process of using the acid for neutralization, the degree ofneutralization of the existing amino group is preferably in the range ofabout 20-100%, and more preferably is about 40-70%. According to asuitable neutralization method, an acid for neutralization such asformic acid, acetic acid, lactic acid and phosphoric acid, a surfactant,deionized water, etc., are added and dispersed into water by ahigh-speed stirring so that an excellent resin of an aqueous dispersionmay be obtained.

Successively, a solvent stripping of the organic solvent having the lowboiling point is performed at about 40-80° C. and at about 30-90 mmHg,and more preferably is performed under a reduced pressure of about 50-70mmHg. Then, organic solvents having a high boiling point over 140° C.,which has been included in the preparation of the cationicelectrodeposition synthetic resin obtained by an epoxy-amino additionreaction, the acrylic cationic electrodeposition resin having an aminogroup, and the fatty acid ester resin synthesized by an esterificationreaction of styrene-allylalcohol copolymer and fatty acid, remains.Meanwhile, organic solvents having the low boiling point such as methylisobutyl ketone, xylene, toluene, methyl ethyl ketone, etc., areremoved.

After implementing the solvent stripping process for making the solidcontent of the aqueous dispersion of the cationic electrodepositionresin being about 20-60% by weight, and more preferably about 30-40% byweight, the aqueous dispersion is filtered through diatomaceous earth insuch a manner that an improved cationic electrodeposition coatingcomposition can be obtained. The average particle size of the improvedcationic electrodeposition coating composition is less than 60 nm andthe organic solvent content is minimized.

The method of preparing the first component of the cationicelectrodeposition coating composition, the cationic electrodepositionresin dispersion has been described above. Herein below, a method ofpreparing the second component, a pigment paste composition will bedescribed.

First, a pigment grinding vehicle for the cationic electrodepositioncoating composition is prepared from about 25-35% by weight ofpolyglycidyl ether of bisphenol A, about 5-12% by weight ofpropyleneglycol monomethyl ether acetate, about 8-15% by weight ofpartially blocked isocyanate cross-linking agent, about 25-40% by weightof ethylene glycol monobutyl ether, about 10-20% by weight of organictertiary amino acid salt and about 0-5% by weight of deionized water.

If the amount of the polyglycidyl ether of bisphenol A used is less thanabout 25% by weight, properties such as corrosion-resistance, waterresistance, etc. are deteriorated, and if the amount of the polyglycidylether of bisphenol A used exceeds 35% by weight, mechanical propertiesof the dried coating layer such as hardness is diminished. Therefore,the amount of the polyglycidyl ether of bisphenol A used is preferablyin the range of about 25-35% by weight, and more preferably about 27-32%by weight.

If the amount of the propyleneglycol monomethyl ether acetate used isless than 5% by weight, the process of melting the polyglycidyl etherresin of bisphenol A is poorly performed. If the amount of thepropyleneglycol monomethyl ether acetate used exceeds 12 percent byweight, the stability of the paint manufactured with the pigmentgrinding vehicle is deteriorated. Therefore, the amount of thepropyleneglycol monomethyl ether acetate used is preferably about 5-12%by weight, and more preferably about 7-10% by weight.

If the amount of the partially blocked isocyanate cross-linking agentused is less than 8% by weight, the hardness of the coating layer islessened. If the amount of the partially blocked isocyanatecross-linking agent used exceeds 15% by weight, the mechanical propertyof the coating layer is lowered due to the increase of the hardness ofthe coating layer. Therefore, the amount of the partially blockedisocyanate cross-linking agent used is preferably in the range of about8-15% by weight, and more preferably about 10-13% by weight.

If the amount of ethyleneglycol monobutyl ether used is less than 25% byweight, the stability of the electrodeposition paint is poor, and if theamount of the ethyleneglycol monobutyl ether used exceeds 40% by weight,the organic solvent content is increased. So, the amount of theethyleneglycol monobutyl ether used is preferably in the range of about25-40% by weight, and more preferably about 30-35% by weight.

If the amount of the organic tertiary amino acid salt used is less than10% by weight, the water-miscibility is insufficient. If the amount ofthe organic tertiary amino acid salt used exceeds 20% by weight, theproperty of water resistance is poor. So, the amount of the organictertiary amino acid salt used is preferably in the range of about 10-20%by weight, and more preferably about 13-16% by weight.

At this time, if the polyglycidyl ether of bisphenol A has an epoxyequivalent weight less than about 900, chemical properties of thecoating layer such as water resistance, corrosion-resistance, etc., arepoor. Therefore, the epoxy equivalent weight of the polyglycidyl etherof bisphenol A used is preferably about 900-1200 (or 1400-2800 byweight-average molecular weight).

The pigment paste composition includes the pigment grinding vehicleprepared by the above-described method, pigment ingredients such ascarbon black or titanium dioxide, a catalyst such as dibutyl tin oxideand an anticorrosive pigment for improving the corrosion-resistance.

In the pigment paste composition, the amount of the pigment grindingvehicle used is in the range of about 15-30% by weight and preferably,about 17-25% by weight. If the amount of the pigment grinding vehicle isless than 15% by weight, a viscosity increases during storing, therebyweakening a storage stability. If the amount of the pigment vehicleexceeds 30% by weight, the storage stability is increased. However, someproperties such as water-resistance, chemical-resistance, etc. of adried film of the cationic electrodeposition coating composition aredeteriorated.

In order to improve the corrosion-resistance of the dried film, ananticorrosive pigment such as a bismuth compound containing bismuthhydroxide, bismuth trioxide, bismuth oxide, etc., aluminum tri-phosphatehydrate, magnesium aluminum hydroxide carbonate hydrate, etc. can beincluded in the pigment paste composition. The amount of theanticorrosive pigment is in the range of about 2-6% by weight, and morepreferably about 3-5% by weight. If the amount of the anticorrosivepigment is less than 2% by weight, the corrosion-resistance of the driedfilm of the cationic electrodeposition coating composition isdeteriorated and if the amount exceeds 6% by weight, the viscosity ofthe pigment increases to generate a coagulating phenomenon duringstoring.

Further, a tin compound such as dibutyl tin oxide can be included in thepigment paste composition as a curing catalyst. The amount used of thetin compound is in the range of about 0.7-2.3% by weight, and morepreferably about 1-2% by weight. If the amount of the tin compound isless than 0.7% by weight, a curing characteristic is weakened and somechanical properties and chemical properties are weakened after dryingthe cationic electrodeposition coating composition. If the amount of thetin compound exceeds 2.3% by weight, the curing density increases afterthe drying and the chemical properties are improved, however, themechanical properties such as impact resistance and flexibility aredeteriorated.

In addition, the ratio of the solid content of the pigment/pigmentgrinding vehicle in the pigment paste composition is in the range ofabout 1/0.20-1/0.45, and more preferably in the range of about1/0.25-1/0.35. If the ratio of the solid content of the pigment/pigmentgrinding vehicle of the pigment paste composition is less than 1/0.20,the mechanical properties and the chemical properties of the dried filmof the cationic electrodeposition coating composition are deteriorated,and if exceeds 1/0.45, the stability of the pigment paste composition isdeteriorated to generate a coagulating phenomenon.

Hereinafter, the present Invention will be explained in more detailreferring to the preferred embodiments. However, the present inventionis not limited to the following embodiments. The parts are by weight andthe percents are by weight too.

SYNTHETIC EXAMPLE 1

A cationic acrylic copolymer resin was manufactured using the followingmixture illustrated in Table 1.

TABLE 1 Ingredients weight parts ethylene glycol monobutyl ether 34.7butyl acrylate 6.2 styrene 29.3 (N,N-dimethyl)aminoethyl methacrylate5.9 2-hydroxyethyl acrylate 11.8 methyl methacrylate 1.8 isobornylmethacrylate 4.1 ethylene glycol monobutyl ether 0.9azo-bisisobutylronitrile 0.7 ethylene glycol monobutyl ether 1.9azo-bisisobutyronitrile 0.7

34.7 parts of ethylene glycol monobutyl ether was introduced into aflask and held under nitrogen atmosphere at 110° C. Then, a mixture of6.2 parts of butyl acrylate, 29.3 parts of styrene, 5.9 parts of(N,N-dimethyl)aminoethyl methacrylate, 11.8 parts of 2-hydroxyethylacrylate, 1.8 parts of methyl methacrylate and 4.1 parts of isobornylmethacrylate at 115° C., was dropped over four hours. Also, a mixture of0.7 parts of azo-bisisobutyronitrile and 1.9 parts of ethylene glycolmonobutyl ether was dropwisely added to the resultant through a funnelover an hour. After the addition, the mixture was held for three hoursto obtain a cationic acrylic copolymer whose amine value was 30-40 andsolid content was 60 percent.

SYNTHETIC EXAMPLE 2

A fatty acid ester resin synthesized by an esterification of astyrene-allylalcohol copolymer and fatty acid was manufactured from thefollowing mixture illustrated in Table 2.

TABLE 2 ingredients weight parts coconut fatty acid 9.9styrene-allylalcohol copolymer 60.3 xylene 1.9 ethylene glycol monobutylether 27.9

After 9.9 parts of palm oil (fatty acid) and 60.3 parts ofstyrene-allylalcohol copolymer were introduced into a flask and heatedto 140° C. to be melted. The resultant mixture was heated to 220° C. andheld at this temperature to obtain a fatty acid ester resin synthesizedby an esterification reaction of styrene-allylalcohol copolymer andfatty acid. The acid value of the fatty acid ester resin was less than 4and the solid content thereof was 70.

SYNTHETIC EXAMPLE 3

A reaction product of manganese phosphate and a phosphoric acid dilutedin an deionized water to 10% was prepared by utilizing the compoundsillustrated in Table 3.

TABLE 3 ingredients weight parts manganese phosphate 4.08 phosphoricacid 1.0 deionized water 35.72

4.08 parts of manganese phosphate and 35.72 parts of deionized waterwere added into a flask and heated to 60° C. After stirring for onehour, 1.0 parts of phosphoric acid was added at 40° C. and thus obtainedproduct was stood for 30 minutes.

EXAMPLE 1

From the mixture having the following ingredients illustrated in Table4, a cationic electrodeposition resin was manufactured.

TABLE 4 Ingredients weight parts EPIKOTE 828CD*¹ 27.1 PLACCEL 205*² 9.7bisphenol A 7.9 methyl isobutyl ketone 2.4 benzyl dimethyl amine 0.15cationic resin containing (N, N-dimethyl)aminoethyl 9.0 methacrylate(synthetic example 1) fatty acid ester resin synthesized by anesterification of 1.6 styrene-allylalcohol copolymer and fatty acid(synthetic example 2) blocked polyisocyanate cross-linking agent*³ 40.5diketimine derived from diethylene triamine and methyl 3.0 isobutylketone (73% of solid content in methyl isobutyl ketone)N-methylethanolamine 2.6 *¹EPIKOTE 828CD is an epoxy resin manufacturedby the reaction of epichlorohydrin and bisphenol A, which may bepurchased from Kumho P&B Co., Ltd. in Korea. The epoxy equivalent weightthereof was approximately 188. *²PLACCEL 205 is a polycaprolactondiolwhich may be purchased from DICEL Corp. in Japan. *³The blockedpolyisocyanate cross-linking agent was manufactured from the mixturehaving the following ingredients. A mixture containingpolymethylene-polyphenyl isocyanate and diphenyl methyl-4,4-diisocyanate(Polymeric MDI (PAPI-135K) which may be purchased from HD POLYURETHANECo., in Korea) was half blocked with diethylene glycol monobutyl ether.Then, the resulting product was reacted with trimethylolpropane at amolar ratio of 3:1 to form the polyurethane cross-linking agent.

An aqueous dispersion of the cationic electrodeposition resin wasprepared from the mixture of the following ingredients illustrated inTable 5.

TABLE 5 ingredients weight parts cationic electrodeposition resinaccording to the present 39.25 example acetic acid 0.45 reaction productof 10% manganese phosphate and 3.5 phosphoric acid cationic surfactant*¹0.53 deionized water 56.27 *¹The cationic surfactant is a commerciallyavailable XS-139, which may be purchased from Air Products and ChemicalInc.

1-(a) Preparation of a Cationic Electrodeposition Resin

27.1 parts of EPIKOTE 828CD, 9.7 parts of PLACCEL 205, 7.9 parts ofbisphenol A and 2.4 parts of methyl isobutyl ketone were introduced intoa reactor. The mixture was then heated to 140° C. under a nitrogenatmosphere. Then, 0.04 parts of benzyl dimethyl amine was added to thereaction mixture, which was heated to 210° C. and was reacted at areflux temperature for thirty minutes to remove water. The resultantmixture was cooled to 160° C. and held in that state for one and halfhours. Then, the resulting mixture was cooled to 145° C. and 0.11 partsof benzyl dimethyl amine was added to the resulting product, which wasreacted at 145° C. for approximately two and half hours to prepare thecationic electrodeposition synthetic resin obtained by an epoxy-aminoaddition reaction. To the cationic electrodeposition synthetic resinobtained by an epoxy-amino addition reaction, 9.0 parts of a cationicresin having (N,N-dimethyl)aminoethyl methacrylate, 1.6 parts of a fattyacid ester resin synthesized by an ester reaction ofstyrene-allylalcohol copolymer and fatty acid and 40.5 parts of ablocked isocyanate cross-linking agent were sequentially and slowlyadded at the same temperature. Next, 3.0 parts of diketimine (73% ofsolid content in methyl isobutyl ketone) derived from diethylenetriamine and methyl isobutyl ketone and 2.6 parts of N-methyl ethanolamine were added to the resultant at 100-110° C., which was held at 125°C. for an hour to obtain the cationic electrodeposition resin.

1-(b) Preparation of an Aqueous Dispersion of the CationicElectrodeposition Resin

56.27 parts of deionized water, 0.45 parts of acetic acid, 3.5 parts ofa reaction product of 10% manganese phosphate with phosphoric acid and0.53 parts of cationic surfactant, XS-139, were successively introducedinto a reactor and homogenized. Then, 39.25 parts of cationicelectrodeposition resin was slowly added and was stirred at a high speedin order to disperse into water. Meanwhile, a solvent stripping processwas performed at 60° C. and under a reduced pressure of approximately 60mmHg in order to remove a low boiling point organic solvent. Then, thewater-dispersed resin was filtered through diatomaceous earth in such amanner that a water-dispersed solution of the cationic electrodepositionresin whose solid content was 36% and average particle size was lessthan 60 nm can be obtained. The organic solvent content in the aqueousdispersion of the obtained cationic electrodeposition resin wasapproximately 0.3% or less.

1-(c) Preparation of a Pigment Grinding Vehicle

A pigment grinding vehicle was prepared by reacting polyglycidyl etherof bisphenol A, a partially blocked isocyanate cross-linking agent andorganic tertiary aminate as illustrated in Table 6 below.

TABLE 6 ingredients weight parts EPIKOTE 3004CD*¹ 29.0 propylene glycolmonomethyl ether acetate 10.0 partially blocked isocyanate cross-linkingagent*² 12.0 ethylene glycol monobutyl ether 33.0 organic tertiaryaminate*³ 14.0 deionized water 2.0 *¹Polyglycidyl ether of bisphenol A(epoxy equivalent weight 900-1200) which may be purchased from Kumho P&BCo., Ltd. in Korea, was used. *²The used partially blocked isocyanatecross-linking agent was prepared by reacting 54.3 parts of2,4-tolueneisocyanate and 40.7 parts of 2-ethyl hexanol at less than 40°C. for three hours, adding 5.0 parts of methyl isobutyl ketone anddiluting. *³The used organic tertiary aminate was manufactured asfollows. 15.5 parts of dimethyl ethanol amine and 56.7 parts of apartially blocked isocyanate cross-linking agent were reacted at a roomtemperature for two hours. The disappearance of NCO peak could beconfirmed at 80° C. Then, 17.4 parts of lactic acid (purity 88%), 3.5parts of deionized water and 7.0 parts of ethylene glycol monobutylether were added and reacted at 60° C. for an hour to obtain the organictertiary aminate.

29.0 parts of EPIKOTE 3004CD and 10.0 parts of propylene glycolmonomethyl ether acetate were added to a reactor and heated to 110-120°C. so as to melt homogeneously. To the resulting product was added 12.0parts of a partially blocked isocyanate cross-linking agent, and theresulting product was held for an hour. Next, 33.0 parts of ethyleneglycol monobutyl ether was added to the resulting product, which washeated to 80-90° C. Thereafter, 14.0 parts of organic tertiary aminateand 2.0 parts of deionized water were added to the resulting product,which was held until the acid value became approximately 0.8 so thepigment grinding vehicle was obtained. At this time, the epoxyequivalent weight of the polyglycidyl ether of bisphenol A was 900-1200.

1-(d) Preparation of the Pigment Paste Composition

A mixture of 0.6 parts of carbon black, 22.05 parts of titanium dioxide,4.51 parts of bismuth trioxide, 45 parts of ion exchanged water, 1.7parts of dibutyl tin oxide, 16.77 parts of aluminum silicate and 25parts of pigment grinding vehicle was ground in a bead mill to have aparticle size of less than 15 μm, thereby obtaining a dispersed productof a pigment paste composition. At this time, the solid content of thepigment paste composition was 50% and the ratio of the solid content ofpigment/pigment grinding vehicle was 1/0.27.

110 parts of thus obtained pigment paste composition, 403 parts of anaqueous dispersion of the cationic electrodeposition resin and 392 partsof deionized water were homogeneously stirred to obtain a dilutedproduct of a cationic electrodeposition coating composition.

EXAMPLE 2

From the mixture having the following ingredients illustrated in Table7, an aqueous dispersion of a cationic electrodeposition resin wasmanufactured.

TABLE 7 ingredients weight parts EPIKOTE 829*¹ 27.1 bisphenol A 17.6xylene 2.4 benzyl dimethyl amine 0.15 cationic resin containing (N,N-dimethyl)aminoethyl 9.0 methacrylate (synthetic example 1) fatty acidester resin synthesized by an esterification of 1.6 styrene-allylalcoholcopolymer and fatty acid (synthetic example 2) blocked polyisocyanatecross-linking agent*² 40.5 diketimine derived from diethylene triamineand methyl 3.0 isobutyl ketone (73% of solid content in methyl isobutylketone) N-methyl ethanolamine 2.6 *¹EPIKOTE 829 is an epoxy resinmanufactured by the reaction of epichlorohydrin and bisphenol A, whichmay be purchased from Kumho P&B Co., Ltd. in Korea. The epoxy equivalentweight thereof was approximately 188. *²The blocked polyisocyanatecross-linking agent was manufactured as follows. Toluene diisocyanate(80/20 2.4/2.6 isomer mixture) is half-blocked by 2-ethyl hexanol. Thusobtained product is reacted with trimethylol propane in a molar ratio of3:1 to prepare a polyurethane cross-linking agent. The cross-linkingagent is present as a solution in a methyl isobutyl ketone.

An aqueous dispersion of the cationic electrodeposition resin wasprepared from the mixture of the following ingredients illustrated inTable 8.

TABLE 8 ingredients weight parts cationic electrodeposition resinaccording to the present 39.00 example lactic acid 1.09 reaction productof 10% manganese phosphate and 3.5 phosphoric acid (synthetic example 3)cationic surfactant*¹ 0.53 deionized water 55.89 *¹The cationicsurfactant is a commercially available XS-139, which may be purchasedfrom Air Products and Chemical Inc.

2-(a) Preparation of a Cationic Electrodeposition Resin

27.1 parts of EPIKOTE 829, 17.6 parts of bisphenol A and 2.4 parts ofxylene were introduced into a reactor. The mixture was then heated to140° C. under a nitrogen atmosphere. Then, 0.04 parts of benzyl dimethylamine was added to the reaction mixture, which was heated to 210° C. andwas reacted at a reflux temperature for thirty minutes to remove water.The resultant mixture was cooled to 160° C. and held in that state forone and half hours. Then, the resulting mixture was cooled to 145° C.and 0.11 parts of benzyl dimethyl amine was added to the resultingproduct, which was reacted at 145° C. for approximately two and halfhours to prepare the cationic electrodeposition synthetic resin obtainedby an epoxy-amino addition reaction. To the cationic electrodepositionsynthetic resin obtained by an epoxy-amino addition reaction, 9.0 partsof a cationic resin having (N,N-dimethyl)aminoethyl methacrylate, 1.6parts of a fatty acid ester resin synthesized by an esterification ofstyrene-allylalcohol copolymer and fatty acid and 40.5 parts of ablocked isocyanate cross-linking agent were sequentially and slowlyadded at the same temperature. Next, 3.0 parts of diketimine (73% ofsolid content in methyl isobutyl ketone) derived from diethylenetriamine and methyl isobutyl ketone and 2.6 parts of N-methyl ethanolamine were added to the resultant at 100-110° C., which was held at 125°C. for an hour to obtain the cationic electrodeposition resin. Then,24.3 parts of blocked isocyanate cross-linking agent and 16.2 parts ofblocked isocyanate cross-linking agent were subsequently and slowlyadded at 90° C. to prepare the low temperature curable cationicelectrodeposition resin.

2-(b) Preparation of an Aqueous Dispersion of the CationicElectrodeposition Resin

55.89 parts of deionized water, 1.09 parts of 88% lactic acid, 0.53parts of cationic surfactant, XS-139 and 3.5 parts of a reaction productof 10% manganese phosphate with phosphoric acid, were successivelyintroduced into a reactor and homogenized. Then, 39.0 parts of cationicelectrodeposition resin was slowly added and was stirred at a high speedin order to disperse into water. Meanwhile, a solvent stripping processwas performed at 60° C. and under a reduced pressure of approximately 60mmHg in order to remove a low boiling point organic solvent. Then, thewater-dispersed resin was filtered through diatomaceous earth in such amanner that an aqueous dispersion of the cationic electrodepositionresin whose solid content was 36% and average particle size was lessthan 60 nm can be obtained. The organic solvent content in the aqueousdispersion of the obtained cationic electrodeposition resin wasapproximately 0.3% or less.

2-c) Preparation of a Pigment Grinding Vehicle

A pigment grinding vehicle was prepared by reacting polyglycidyl etherof bisphenol A, a partially blocked isocyanate cross-linking agent andorganic tertiary aminate as illustrated in Table 9 below.

TABLE 9 ingredients weight parts EPIKOTE 3004CD*¹ 29.0 propylene glycolmonomethyl ether acetate 10.0 partially blocked isocyanate cross-linkingagent*² 12.0 ethylene glycol monobutyl ether 33.0 organic tertiaryaminate*³ 14.0 deionized water 2.0 *¹Polyglycidylether of bisphenol A(epoxy equivalent weight 900-1200) which may be purchased from Kumho P&BCo., Ltd. in Korea, was used. *²The used partially blocked isocyanatecross-linking agent was prepared by reacting 54.3 parts of2,4-tolueneisocyanate and 40.7 parts of 2-ethyl hexanol at less than 40°C. for three hours, adding 5.0 parts of methyl isobutyl ketone anddiluting. *³The used organic tertiary aminate was manufactured asfollows. 15.5 parts of dimethyl ethanol amine and 56.7 parts of apartially blocked isocyanate cross-linking agent were reacted at roomtemperature for two hours. The disappearance of NCO peak could beconfirmed at 80° C. Then, 17.4 parts of lactic acid (88%), 3.5 parts ofdeionized water and 7.0 parts of ethylene glycol monobutyl ether wereadded and reacted at 60° C. for an hour to obtain the organic tertiaryaminate.

29.0 parts of EPIKOTE 3004CD and 10.0 parts of propylene glycolmonomethyl ether acetate were added to a reactor and heated to 110-120°C. so as to melt homogeneously. To the resulting product was added 12.0parts of a partially blocked isocyanate cross-linking agent, and theresulting product was held for an hour. Next, 33.0 parts of ethyleneglycol monobutyl ether was added to the resulting product, which washeated to 80-90° C. Thereafter, 14.0 parts of organic tertiary aminateand 2.0 parts of deionized water were added to the resulting product,which was held until the acid value became approximately 1 so thepigment grinding vehicle having a good dispersibility and storagestability was obtained.

2-(d) Preparation of the Pigment Paste Composition

A mixture of 0.6 parts of carbon black, 22.05 parts of titanium dioxide,4.51 parts of bismuth trioxide, 45 parts of ion exchanged water, 1.7parts of dibutyl tin oxide, 16.77 parts of aluminum silicate and 25parts of pigment grinding vehicle was ground in a bead mill to have aparticle size of less than 15 μm, thereby obtaining a dispersed productof a pigment paste composition. At this time, the solid content of thepigment paste composition was 50% and the ratio of the solid content ofpigment/pigment grinding vehicle was 1/0.27.

110 parts of thus obtained pigment paste composition, 403 parts of anaqueous dispersion of the cationic electrodeposition resin and 392 partsof deionized water were homogeneously stirred to obtain a dilutedproduct of the cationic electrodeposition coating composition.

COMPARATIVE EXAMPLE 1

A dispersed solution of a cationic electrodeposition resin the same asthat of Example 1 was prepared using the resin synthesized by the samemethod as mentioned in Example 1, except that a cationic resin having(N,N-dimethyl)aminoethyl methacrylate (Synthetic Example 1), a fattyacid ester resin synthesized by an ester reaction ofstyrene-allylalcohol copolymer and fatty acid (Synthetic Example 2) anda reaction product of 10% manganese phosphate and phosphoric acid(Synthetic Example 3) were not added to the cationic electrodepositonresin composition of Example 1-(a).

In addition, a pigment paste composition was prepared by the same methodas mentioned in Example 1-(d), except that bismuth trioxide was notadded and 0.5 parts of dibutyl tin oxide was added. Then, a cationicelectrodeposition coating composition was prepared by the same method asmentioned in Example 1.

COMPARATIVE EXAMPLE 2

A dispersed solution of a cationic electrodeposition resin the same asthat of Example 2 was prepared using the resin synthesized by the samemethod as mentioned in Example 2, except that a cationic resin having(N, N-dimethyl)aminoethyl methacrylate (Synthetic Example 1) and a fattyacid ester resin synthesized by an ester reaction ofstyrene-allylalcohol copolymer and fatty acid (Synthetic Example 2) werenot added to the cationic electrodeposition resin composition of Example2-(a).

In addition, a pigment paste composition was prepared by the same methodas mentioned in Example 1-(d), except that bismuth trioxide was notadded and 0.5 parts of dibutyl tin oxide was added. Then, a cationicelectrodeposition coating composition was prepared by the same method asmentioned in Example 2.

By using the electrodeposition coating compositions obtained fromExamples 1 and 2 and Comparative Examples 1 and 2, an electrodepositioncoating was performed at 28° C. and at a voltage of 200V for threeminutes, and at a curing temperature of 165° C. for twenty minutes. Theproperties of the obtained film having the thickness of 20 μm wereexamined. The testing results on the film are illustrated in Table 10.

TABLE 10 Comparative Comparative Example 1 Example 2 Example 1 Example 2appearance ⊚ ⊚ ⊚ ⊚ gloss 64 63 73 75 (60° glossmeter) pencil hardness 3H3H HB HB (Mitsubishiuni) adhesion*¹ ⊚ ⊚ ⊚ ⊚ impact-resistance*⁷ OK OK OKOK (½″ 500 g x 50 cm) flexible-resistance*⁸ OK OK OK OK (MandrelConical) corrosion resistance 1*² <0.5 mm <0.5 mm >5 mm >5 mm corrosionresistance 2*³ <0.2 mm <0.5 mm >5 mm >5 mm water-resistance*⁴ ⊚ ⊚ X Xsolvent-resistance*⁵ ⊚ ⊚ Δ Δ yellowing resistance*⁶ ⊚ ⊚ Δ Δweather-resistance*⁹ ⊚ ⊚ Δ Δ *Note: ⊚; excellent, ◯; good, Δ; common, X;bad *¹cross-cut: A taping test was performed by cross-cutting the filmin a size of 1 mm × 1 mm within a size of 1 cm × 1 cm. *²corrosionresistance 1: After spraying 5% NaCl solution at 35° C. over a thousandhours and allowing it to stand for twenty-four hours, a taping test wasperformed. *³corrosion resistance 2: After immersing the film in 5% NaClsolution at 50° C. for two-hundred forty hours, a taping test wasperformed. *⁴water-resistance: After immersing the film in hot-water of50° C. for two-hundred forty hours, the external appearance of thecoating layer was observed. *⁵solvent-resistance: After reciprocatingrubbing the film twenty times with methyl isobutyl ketone solvent, thepresence of any abnormality in the coating layer was observed.*⁶yellowing resistance: After coating a small amount of white enamelpaint on the electrodeposition coated test plate, curing at 150° C. formore than forty minutes and drying, the degree of yellowing resistancein the top coating was tested. *⁷impact-resistance: The test wasexecuted five times by means of an impact-resistance tester manufacturedfrom Dupont Co. wherein a coating layer which was not destroyed morethan four times was regarded as OK. *⁸flexible-resistance: The test wasexecuted five times by means of a Mandrel Conical flexible-resistancetester wherein a coating layer which did not crack for more than fourtimes was regarded as OK. *⁹weathering resistance: Gloss and colordifference were tested by means of a Weather-O-Meter (W.O.M) for twohundred hours.

As shown in Table 10, the coating layer formed by using the cationicelectrodeposition coating composition of Examples 1 and 2 using thecationic resin having (N,N-dimethyl)aminoethyl metacrylate (SyntheticExample 1), the fatty acid ester resin synthesized by an esterificationof styrene-allylalcohol copolymer and fatty acid (Synthetic Example 2)and manganese phosphate (Synthetic Example 3), along with a pigmentpaste composition including bismuth compound instead of lead compound,has an excellent corrosion resistance, appearance, yellowing resistance,weather resistance, mechanical properties, etc.

Meanwhile the coating layer formed by using the cationicelectrodeposition coating compositions of Comparative Examples 1 and 2without employing the cationic resin and the fatty acid ester resin, hasa good appearance but not as good as those of Examples 1 and 2, and hasan inferior level of corrosion resistance, yellowing resistance andweather resistance as those of Examples 1 and 2. Moreover, from theaspect of pencil hardness, the coating layer formed by using thecationic electrodeposition coating composition of Examples 1 and 2 isbetter than that of Comparative Examples 1 and 2.

As described above, an aqueous dispersion of the cationicelectrodeposition resin in the cationic electrodeposition coatingcomposition of the present invention includes a metal salt for improvinga corrosion resistance and a minimized amount of organic solvents lessthan 0.3%. A dried film formed by electrodepositing a composition usinga bismuth compound instead of a lead compound in a pigment pastecomposition, has a good chemical properties such as acorrosion-resistance and an improved physical properties such as anexternal appearance, yellowing resistance, weather resistance, etc.while keeping the remaining excellent characteristics as it stands.

Even when a cationic electrodeposition coating composition is preparedby employing the aqueous dispersion of the cationic electrodepositionresin of the present invention along with the conventional pigment pastecomposition, the corrosion resistance is improved and the amount of theorganic solvent used can be reduced. And even when a cationicelectrodeposition coating composition is prepared by employing thepigment paste composition of the present invention along with theconventional aqueous dispersion of the cationic electrodeposition resin,a lead-free film can be formed and film characteristics such as thecorrosion resistance, chemical resistance, etc. can be improved.

Accordingly, even though excellent effects can be obtained when both ofthe aqueous dispersion of the cationic electrodeposition resin and thepigment paste composition are used for the preparation of the cationicelectrodeposition coating composition, an inclusion of one of the twocompositions results in an improved effect. Therefore, the coatingcomposition including one of the two compositions is included in thepresent invention.

While the present invention is described in detail referring to theattached embodiments, various modifications, alternate constructions andequivalents may be employed without departing from the true spirit andscope of the present invention.

What is claimed is:
 1. A pigment paste composition comprising (a) about15-30% by weight of pigment grinding vehicle (b) about 26% by weight ofan anticorrosive pigment and (c) about 0.7-2.3% by weight of dibutyl tinobxide, a ratio of solid content of said pigment/pigment grindingvehicle being about 1/0.2-1/0.45.
 2. A pigment paste composition asclaimed in claim 1, wherein said pigment grinding vehicle is obtainablefrom about 25-35% by weight of polyglycidyl ether of bisphenol A, about5-12% by weight of propyleneglycol monomethyl ether acetate, about 8-15%by weight of partially blocked isocyanate cross-linking agent, about25-40% by weight of ethylene glycol monobutyl ether, about 10-20% byweight of organic tertiary amino-acid salt and about 0-5% by weight ofdeionized water.
 3. A cationic electrodeposition coating compositioncomprising: a resin disperson of a cationic electrodeposition; and apigment paste composition comprising (a) about 15-30% by weight ofpigment grinding vehicle (b) about 2-6% by weight of an anticorrosivepigment and (c) about 0.7-2.3% by weight of dibutyl tin obxide, a ratioof solid content of said pigment/pigment grinding vehicle being about1/0.2-1/0.45.
 4. A cationic electrodeposition coating composition asclaimed in claim 3, wherein said anticorrosive pigment is at least oneselected from the group consisting of bismuth hydroxide, bismuthtrioxide, bismuth oxide, aluminum tri-polyphosphate hydrate andmagnesium aluminum hydroxide carbonate hydrate.